Liquid level indicator



Dec. 29, 1964 H. M. DIECKAMP 3,163,843

LIQUID LEVEL INDICATOR Filed Oct. 2, 1961 2 Sheets-SheeiI l ATTORNEY Dec- 29, 1964 H M. DIECKAMP 3,163,843

LIQUID LEVEL INDICATOR 2 Sheets-Sheet 2 Filed Oct. 2, 1961 N .mi

INVENTOR. HERMAN M. DIECKAMP` M4@ ATTORNEY 3,163,843 LIQUID LEVEL ENBECAGR Herman M. Dieclramp, Canoga Parli, Calif., assigner to North American Aviation, line. Filed Oct. 2, 196i, Ser. No. 142,321 2 Claims. (Cl. 340-1) This inven-tion relates to means for automatically indicating the liquid level in a vessel and more particularly tiran electric apparatus for effecting such measurement.

When measuring the level of corrosive or radio-active liquids, or liquids operating at high temperatures, remote measurement is necessary. In nuclear systems and in other industrial applications, space considerations require that level-measuring equipment remain external to the vessel. Also, economies can be achieved and maintenance problems reduced by minimizing the number of mechanical or electrical components operating within the vessel containing the liquid.

It is, therefore, an object or this invention to provide electronic means for automatically and remotely measuring the level of a liquid in a vessel.

Another object of this invention is to provide a liquid` level detection system having substantially all electronic circuitry located external to the vessel and requiring no mechanical moving parts within the vessel.

These and other objects of the present invention will be more apparent from the following description and claims taken in conjunction with the accompanying drawings, made a part hereof, in which:

FIG. l is a simplied schematic diagram showing :the preferred embodiment of this invention in block form;

FIG. 2 is a schematic circuit diagram constructed in accordance with the teachings of this invention.

In accordance with this invention, the level of a liquid is measured automatically and remotely by transmitting mechanical vibrations through a rigid member which extends substantially throughout the depth of the liquid and detecting the relative positions of vibrations reflected both from the surface of such liquid and the submersed end of the member. The Vibrations are intermittently induced into the member from a reversible energy conversion device actuated by an ultrasonic voltage signal, received from a source external to the vessel. The conversion device also transmutes the reflected vibrations to electrical pulses. Electronic means is provided for measuring the liquid depth by comparing the relative positions of the waveforms of the voltage signal and refiected pulses.

Referring to the drawings, the preferred embodiment of the present invention is illustrated and will be hereinafter described. In FIG. l, operation of the -systemis initiated by a low-power ultrasonic oscillator 4 generating a sinusoidal voltage signal in the 100 kilocycle to. l0 megacycle frequency range. The oscillator output is lfed through conductor @5 to a gate circuit 8 which functions as an electronic switch, intermittently passing the operating signal through at a predetermined period and repetition rate. The operating signal from oscillator 4 is blocked in gate 8, since this circuit requires two concurrent input signals to produce an output signal. Multivibrator lit provides the additional input signal, hereinafter referred to as the control signal, which triggers gate AS at a lixed rate, thereby regulating the passage of the operating signal to the output of the gating circuit.

The operating signal from gate is applied through conductor t2 to electro-mechanical transducer i4. Transducer 14 preferably employs a piezoelectric quartz crystal 16 positioned between plane-parallel'electrodes i3 which contact one pair of crystal faces. The operating signal is received at electrodes 18 and the crystal becomesenergized, thus producing a mechanical stress and displacef submerged end 28 of probe 20. Oscilloscope 38 is suit- Y fluence the cathode potential. However, when input sig- Patenten nee. as, ieee ment on a second pair `of crystal faces. In this manner,

the operating signal is converted to mechanical vibrations Y ducer 14. As the pulse travels along probe 2li, there is an abrupt change in probe impedance and a concomitant Variation in pulse transmission characteristic at the .liquid surface 26, and at the end 23 of probe 2%. `This change in impedance produces retiected transverse pulses at the liquid surface 2d and at thesubmerged end 280i probe 20, which are smaller in amplitude than the applied pulse. These retlected transverse pulses are 'propagated back to transducer 14 Where they are converted to electrical pulses at the original ultrasonic frequency.' Both reflected pulses are next fed through conductors 30 and 32 to ampliiier 34 for amplification, and then to the vertical detlection plates 36 of oscilloscope 38. Y

In addition to being connected to transducer 1,4, the output of gate 8 is connected to the inputs of amplier 34 and sweep generator 4t). Therefore, When the operating signal is initially fed to transducer 14, it is simultane-V ously applied through conductors 42, 32. and 44 to the inputs of sweep generator 4t) and amplifier 34. It is amplilied and then fed to oscilloscope 3S. In response to the operating signal, sweep generator 4G produces a saw tooth voltage which energizes the horizontal deflection plates 46 in oscilloscope 38, thereby providing a linear time base therein. Thus, the circuit is synchronized to display on oscilloscope 38 the Wave forms of the operating signal and the reiiected pulses from the liquid surface 26 and the ably calibrated to measure the depth of liquid 22 as a function of the relative positions of these Wave forms on its screen. Y

A more detailed understanding of this invention can be had by now turning to the schematic diagram of FIG. 2. Ultrasonic oscillator 4 is a low-power, tuned-grid type and, as mentioned hereinbefore, produces a voltage signal which initiates operation of the system. Currentrto operate oscillator 4 is supplied from alternating current source 4S, which is coupled through transformerrtl to resonant circuit 52. The magnitudes of inductance coil 54'and variable capacitancep are selected to provide a one megacycle sinusoidal voltage signal which is fed to the grid of triode 5S, wherein it undergoes ampliiic'ation.v

through conductor ti to multigrid or parallel gate would be suitable suliysttutes. The` cathode-coupled gate 8 employs two triodes 62 and."

64, which normally conduct at saturation. In operation,

f cutoif of either triode 62 or 64 by an input signal from oscillator 4 or multivibrator it) respectively, does notinnals arrive simultaneously at grids dll and 66, both triodes It is contemplated that an operating signal of l0 microseconds duration is adequate, but this is dependent upon Vthe1-requirements or" the particular.

system. l Y

f' Amultivibrator is essentially a free-runningoscillator, proyA conventional free-running .multivibrator l@ supplies a control signal to grid 'of'triode 64 in gate 8; This viding intermittent output pulses for triggering gate 3. Other multivibrator circuits suitable for this purpose include the One Shot Multivibrator and the Eccles-Jordan Trigger Circuit. The delay time between output pulses from the multivibrator is set by the time constant of resistances 70 and 72 and capacitances 74 and 76. For equal delays between output pulses, the time constant of resistance 70 and capacitance 76 must equal that of resistance 72 and capacitance 74. To improve t-he frequency stability of multivibrator and to insure that it will be triggered on every nth pulse, an A.C. power source 78, supplies :a synchronizing sinusoidal voltage -as shown. This voltage forces the -period to be equal to a multiple or submultiple of the ysynchronizing frequency.

Transducer 14 utilizes a piezoelectric, X-cut, quartz crystal 15 disposed between plane-parallel electrodes 1S adjoining one pair of the crystal faces. The operating signal from gate S is conveyed through conductor 12 and applied to electrodes 18. in response, mechanical vibrations -are produced -on an alternate pair of crystal faces. These vibrations become very large at the mechanical resonant frequency of the crystal.

A quartz dielectric is preferable because of its inherent stability with time and temperature, which ensures a constant resonant frequency. The vhigh figure of merit (Q) of quartz, l0,000-500,000, accounts for this desirable property. Other suitable dielectrics for this application are crystals of rochelle salts, amomnium tartrate, and barium titanate.

Optimum energy transfer from transducer 14 to probe is achieved by providing a high coupling efficiency therebetween. This is accomplished by matching the crystal and probe irnpedances through proper selection of their relative sizes and by utilizing a hard material for probe 20, e.g., steel or quartz. In this manner, the amplitude of the crystal vibrations is substantially maintained in probe 20.

The operating signal and reflected pulses are amplified in a high frequency, linear, class A operated pentode ampliiier 34, and applied through conductors 80 to the vertical deflection plates 36 of a conventional cathode ray oscilloscope 38 for presentation. Sweep generator 40 simultaneously applies a one megacycle saw tooth voltage through conductors 82 to horizontal deflection plates 46, thereby imparting horizontal travel to the electron beam of oscilloscope 3S. A triggered vacuum tube sweep generator is preferred, since it is particularly adaptable to providing a high frequency sweep wave in response to the operating signal.

Although `the invention has :been described and illustrated in detail, it is to he clearly understood that the same is by way of illustration and example only and is not to be taken by Way of limitation, the spirit and scope of this invention being limited only by the terms of the appended claims.

Having described the invention, what is claimed is:

1. A liquid level indicator comprising:

(a) a source of ultrasonic :frequency electrical energy,

(b) first means transmuting .said electrical energy to corresponding signal mechanical vibrations,

(c) second means intermitten-tly feeding said electrical energy to said rst means,

(d) third means cooperating wi-th said first means and having at least one end submersed in a liquid,

(e) said third means conducting said signal vibrations and further conducting respective mechanical vibrations reflected frorn the surface ofthe liquid and from said submersed end,

(f) said first means further transmuting said reflected mechanical vibrations to corresponding electrical pulses, 'and (g) fourth means comparing the relative positions of said electrical energy and said electrical pulses so that the level of the liquid is determined.

2. A liquid level indicator comprising:

(a) an ultrasonic oscillator generating an alternating voltage signal,

( b) a piezoelectric crystal transmuting said alternating voltage signal to corresponding signal mechanical vibrations,

(c) a gate circuit electrically connected between said oscillator and said crystal,

(d) a multivibrator circuit electrically connected to said gate circuit,

(e) said gate circuit intermittently feeding said voltage signal to said crystal in response to a periodic control signal received from said multivibrator circuit,

(f) an elongated probe having a first end submersed in a liquid and a second end cooperating with said crystal,

(g) said probe conducting said signal vibrations and further conducting respective mechanical vibrations reflected from the surface of the liquid and from said submersed end,

(lz) said crystal further transmuting said reiiected mechanical vibrations to corresponding electrical pulses, `and (i) an oscilloscope means electrically connected to said crystal so that the relative positions of said corresponding electrical pulses are indicated.

References Cited by the Examiner UNlTED STATES PATENTS 2,709,918 7/55 Yetter 73-.290 2,998,723 9/61 Smith etial. 73--290 3,080,752 3/63 Rich 73-290 3,100,994 8/63 Junger 73-290 FOREIGN PATENTS l, 156 6/ 5 6 Great Britain.

829,741 3/ 60 Great Britain.

CHESTER L. JUSTUS, Primmy Examiner.

KATHLEEN CLAFFY, Examiner. 

1. A LIQUID LEVEL INDICATOR COMPRISING: (A) A SOURCE OF ULTRASONIC FREQUENCY ELECTRICAL ENERGY, (B) FIRST MEANS TRANSMUTING SAID ELECTRICAL ENERGY TO CORRESPONDING SIGNAL MECHANICAL VEBRATIONS, (C) SECOND MEANS INTERMITTENTLY FEEDING SAID ELECTICAL ENERGY TO SAID FIRST MEANS, (D) THIRD MEANS COOPERATING WITH SAID FIRST MEANS AND HAVING AT LEAST ONE END SUBMERSED IN A LIQUID, 